High-side energy delivery through a single-quadrant thyristor triggered with a current-limiting switch

ABSTRACT

A cardiac rhythm management system includes an implantable cardiac rhythm management device that includes a defibrillation energy delivery circuit. The defibrillation energy delivery circuit provides high side energy delivery through a single-quadrant thyristor switch that is triggered by a current-limiting transistor switch. The defibrillation energy delivery circuit requires fewer electronic components, reducing the size and/or cost of the implantable cardiac rhythm management device. For example, the single-quadrant thyristor, designed to conduct and latch in only one quadrant (e.g., quadrant III) and having appropriate dV/dt and voltage blocking capabilities, may eliminate the need for additional series-coupled semiconductor devices. In another example, current-limiting is designed into, or inherent in, the semiconductor device triggering the single-quadrant thyristor, thereby eliminating the need for additional current-limiting circuits.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.09/966,643, filed on Sep. 28, 2001 now U.S. Pat. No. 6,647,294, which isa continuation of U.S. patent application Ser. No. 09/525,487, filed onMar. 15, 2000, now issued as U.S. Pat. No. 6,311,087, the specificationsof which are incorporated herein by reference.

TECHNICAL FIELD

The present system relates generally to a system delivering high voltageenergy, and particularly, but not by way of limitation, to a cardiacrhythm management system including a defibrillation energy deliverycircuit having a high-side energy delivery through a single-quadrantthyristor triggered with a current-limiting switch.

BACKGROUND

When functioning properly, the human heart maintains its own intrinsicrhythm, and is capable of pumping adequate blood throughout the body'scirculatory system. However, some people have irregular cardiac rhythms,referred to as cardiac arrhythmias. Such arrhythmias result indiminished blood circulation. One mode of treating cardiac arrhythmiasuses drug therapy. Anti-arrhythmic drugs are often effective atrestoring normal heart rhythms. However, drug therapy is not alwayseffective for treating arrhythmias of certain patients. For suchpatients, an alternative mode of treatment is needed. One suchalternative mode of treatment includes the use of a cardiac rhythmmanagement system. Portions of such systems are often implanted in thepatient and deliver therapy to the heart.

Cardiac rhythm management systems include, among other things,pacemakers, also referred to as pacers. Pacers deliver timed sequencesof low energy electrical stimuli, called pace pulses, to the heart, suchas via an intravascular leadwire or catheter (referred to as a “lead”)having one or more electrodes disposed in or about the heart. Heartcontractions are initiated in response to such pace pulses (this isreferred to as “capturing” the heart). By properly timing the deliveryof pace pulses, the heart can be induced to contract in proper rhythm,greatly improving its efficiency as a pump. Pacers are often used totreat patients with bradyarrhythmias, that is, hearts that beat tooslowly, or irregularly.

Cardiac rhythm management systems also include cardioverters ordefibrillators that are capable of delivering higher energy electricalstimuli to the heart. Defibrillators are often used to treat patientswith tachyarrhythmias, that is, hearts that beat too quickly. Suchtoo-fast heart rhythms also cause diminished blood circulation becausethe heart isn't allowed sufficient time to fill with blood beforecontracting to expel the blood. Such pumping by the heart isinefficient. A defibrillator is capable of delivering a high energyelectrical stimulus that is sometimes referred to as a defibrillationcountershock (“shock”). The shock interrupts the tachyarrhythmia,allowing the heart to reestablish a normal rhythm for the efficientpumping of blood. In addition to pacers, cardiac rhythm managementsystems also include, among other things, pacer/defibrillators thatcombine the functions of pacers and defibrillators, drug deliverydevices, and any other implantable or external systems or devices fordiagnosing or treating cardiac arrhythmias.

One problem faced by cardiac rhythm management systems is in deliveringthe high energy defibrillation shock. In one example, atransformer-coupled dc-to-dc voltage converter transforms a batteryvoltage (e.g., battery voltages approximately between 1.5 Volts and 6.5Volts) up to a high defibrillation voltage (e.g., defibrillationvoltages up to approximately 1000 Volts). The energy associated withthis high defibrillation voltage is typically stored on a storagecapacitor. A defibrillation energy delivery circuit delivers thedefibrillation energy from the storage capacitor to defibrillationleadwires and defibrillation electrodes associated with the heart. Uponreceiving this defibrillation energy via the defibrillation electrodes,the heart resumes normal rhythms if the defibrillation therapy issuccessful.

The defibrillation energy delivery circuit typically includes numerousdiscrete electronic components that must be capable of withstanding thelarge voltages associated with the defibrillation energy beingdelivered. These numerous discrete electronic components in thedefibrillation energy delivery circuit occupy considerable space in theimplantable cardiac rhythm management device. In order to improvepatient comfort and aesthetics, however, the implantable cardiac rhythmmanagement device should be small sized. Thus, a need exists for, amongother things, reducing the size and/or cost of the defibrillation energydelivery circuit.

SUMMARY OF THE INVENTION

This document describes, among other things, portions of a cardiacrhythm management system including an implantable cardiac rhythmmanagement device that includes a defibrillation energy deliverycircuit. The defibrillation energy delivery circuit provides high sideenergy delivery through a single-quadrant thyristor switch that istriggered by a current-limiting transistor switch. The defibrillationenergy delivery circuit requires fewer electronic components, reducingthe number of assembly processing steps, cost and physical size of theimplantable cardiac rhythm management system. For example, thesingle-quadrant thyristor is designed for conduction/latching in asingle quadrant (e.g., quadrant III) and provides the necessary voltageblocking capabilities that can be used to eliminate the need foradditional series coupled voltage blocking semiconductor devices. Inanother example, current-limiting is designed into, or inherent in, thesemiconductor device triggering the single-quadrant thyristor, therebyeliminating the need for additional current-limiting circuits.

This document describes, among other things, a cardiac rhythm managementsystem. In one embodiment, the cardiac rhythm management system includesa cardiac rhythm management device. The cardiac rhythm management deviceincludes a defibrillation energy delivery circuit. The defibrillationenergy delivery circuit includes a first input terminal, receiving afirst power supply, and a first single-quadrant thyristor, coupledbetween the first input terminal and a first output terminal.

In another embodiment, the cardiac rhythm management system includes adefibrillation energy delivery circuit. The defibrillation energydelivery circuit includes a first input terminal, receiving a firstpower supply. The defibrillation energy delivery circuit also includes afirst switch, coupled between the first input terminal and a firstoutput terminal. The defibrillation energy delivery circuit furtherincludes a first current-limiting field-effect transistor (FET), coupledto the gate terminal of the first switch and sinking a triggeringcurrent.

This document also describes, among other things, a method of deliveringdefibrillation energy. The method includes receiving an input voltage,triggering a thyristor enabling single-quadrant conduction/latching, andcoupling the input voltage to an output terminal using the enabledthyristor. These and other aspects of the present system and methodswill become apparent upon reading the following detailed description andviewing the accompanying drawings that form a part thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing illustrating generally one embodiment ofportions of a cardiac rhythm management system and an environment inwhich it is used.

FIG. 2 is a schematic drawing illustrating generally one embodiment of acardiac rhythm management device, which is coupled to a heart, andcertain aspects of the device.

FIG. 3 is a schematic/block diagram illustrating generally oneconceptual embodiment of portions of a defibrillation therapy circuit.

FIG. 4A is a graph illustrating generally one embodiment of a portion ofa current vs. voltage characteristic of a triac, with the four quadrantslabeled I, II, III, and IV.

FIG. 4B is a graph illustrating generally one embodiment of a portion ofa current vs. voltage characteristic of a single-quadrant thyristor,with the four quadrants labeled I, II, III, and IV.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which is shown byway of illustration specific embodiments in which the invention may bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to practice the invention, and it is tobe understood that the embodiments may be combined, or that otherembodiments may be utilized and that structural, logical and electricalchanges may be made without departing from the spirit and scope of thepresent invention. The following detailed description is, therefore, notto be taken in a limiting sense, and the scope of the present inventionis defined by the appended claims and their equivalents. In thedrawings, like numerals describe substantially similar componentsthroughout the several views. Like numerals having different lettersuffixes represent different instances of substantially similarcomponents. In this document, “and/or” refers to non-exclusive “or”(e.g., “A and/or B” includes each of “A but not B.” “B but not A,” and“A and B”).

The present methods and apparatus will be described in applicationsinvolving implantable medical devices including, but not limited to,implantable cardiac rhythm management systems such as pacemakers,cardioverter/defibrillators, pacer/defibrillators, and biventricular orother multi-site coordination devices. However, it is understood thatthe present methods and apparatus may be employed in unimplanteddevices, including, but not limited to, external pacemakers,cardioverter/defibrillators, pacer/defibrillators, biventricular orother multi-site coordination devices, monitors, programmers andrecorders.

General System Overview and Examples

This document describes, among other things, high-side energy deliverythrough a single-quadrant thyristor triggered with a current limitingswitch. The present cardiac rhythm management (CRM) system provides,among other things, an implantable CRM device. The CRM device includes adefibrillation energy delivery circuit capable of delivering high energyusing fewer electronic components. This allows a smaller sized CRMdevice.

FIG. 1 is a generalized schematic diagram illustrating generally, by wayof example, but not by way of limitation, one embodiment of a portion ofa CRM system 100. Various embodiments of system 100 include external orimplantable pacer/defibrillators, cardioverters, defibrillators, anycombination of the foregoing, or any other system using or maintainingcardiac rhythms.

In the embodiment of FIG. 1, CRM system 100 includes a CRM device 105coupled to heart 110 via one or more endocardial or epicardialleadwires, such a pacing leadwire or a defibrillation leadwire 115.Defibrillation leadwire 115 includes one or more defibrillationelectrodes, such as for delivering defibrillation countershock (“shock”)therapy via first defibrillation electrode 120A and/or seconddefibrillation electrode 120B. Defibrillation leadwire 115 may alsoinclude additional electrodes, such as for delivering pacing therapy viafirst pacing electrode 125A (e.g., a “tip” electrode) and/or secondpacing electrode 125B (e.g., a “ring” electrode). Defibrillationelectrodes 120A–B and pacing electrodes 125A–B are typically disposed inor near one or more chambers of heart 110.

In the embodiment of FIG. 1, defibrillation leadwire 115 includesmultiple conductors that are insulated from each other for providingindependent connections between each electrode and cardiac rhythmmanagement device 105. In one embodiment, the defibrillation leadwire issecured to heart 110, such as by a corkscrew, a barb, or similarmechanism at or near first pacing electrode 125A. In another embodiment,CRM device 105 includes a hermetically sealed casing, a portion of whichprovides a conductive electrode that operates in conjunction with atleast one of the electrodes disposed in heart 110 for delivering pacingpulses and/or defibrillation countershocks and/or sensing electricalheart activity signals.

In one embodiment, CRM system 100 includes a remote user interface, suchas programmer 150, which permits communication with CRM device 105 usingtelemetry wand 155 or other communication device. Programmer 150provides information to a physician or other caregiver, such as using agraphical user interface on a screen display, or providing data using astrip chart recorder, or by any other technique. Programmer 150 alsoreceives user input, such as for programming and/or controlling thefunctionality of programmer 150 and/or CRM device 105.

Example Cardiac Rhythm Management Device

FIG. 2 is a schematic diagram illustrating generally, by way of example,but not by way of limitation, one embodiment of portions of device 105,which is coupled to heart 110. Device 105 includes a power source 200,heart signal sensing circuit(s) 205, defibrillation therapy circuit(s)215, a controller 220, and a communication circuit 225 for communicatingwith programmer 150 via telemetry device 155.

The heart signal sensing circuits 205 are coupled by one or more leads115 to one or more electrodes associated with heart 110 for receiving,sensing, and/or detecting electrical heart signals. Such atrial and/orventricular heart signals correspond to heart contractions. Such heartsignals include normal rhythms, and abnormal rhythms includingtachyarrhythmias, such as fibrillation, and other activity. Atrialsensing circuit 205 provides one or more signals to controller 220, vianode/bus 230, based on the received heart signals.

In one embodiment, defibrillation therapy circuit(s) 215 providecardioversion/defibrillation therapy, as appropriate, to the heartelectrodes 120A–B. Controller 220 controls the delivery ofdefibrillation therapy by defibrillation therapy circuit(s) 215 based onheart activity signals received by sensing circuit(s) 205. Controller220 may further control the delivery of pacing therapy such as by apacing therapy circuit (not shown) via pacing electrodes 125A–B.Controller 220 includes various modules, which are implemented either inhardware or as one or more sequences of steps carried out on amicroprocessor or other controller. Such modules may be conceptualizedseparately, but it is understood that the various modules of controller220 need not be separately embodied, but may be combined and/orotherwise implemented, such as in software/firmware.

In general terms, sensing circuit(s) 205 sense electrical signals fromheart tissue in contact with the catheter lead(s) 115 to which sensingcircuit(s) 205 are coupled. Sensing circuit(s) 205 and/or controller 220process these sensed signals. Based on these sensed signals, controller220 issues control signals to therapy circuit 215, if necessary, for thedelivery of electrical energy (e.g., defibrillation pulses) to theappropriate electrodes of lead 115. Controller 220 may include amicroprocessor or other controller for execution of software and/orfirmware instructions. The software of controller 220 may be modified(e.g., by remote external programmer 150) to provide differentparameters, modes, and/or functions for the implantable device 105 or toadapt or improve performance of device 105.

FIG. 3 is a schematic/block diagram illustrating generally, by way ofexample, but not by way of limitation, one conceptual embodiment ofportions of defibrillation therapy circuit 215. In this embodiment,defibrillation therapy circuit 215 includes a defibrillation energygenerator circuit 300 and a defibrillation energy delivery circuit 305.In one example, defibrillation energy generator 300 includes atransformer-coupled dc-to-dc voltage converter that transforms a voltageprovided by power source 200 (e.g., source voltages of approximatelybetween 1.5 Volts and 6.5 Volts) up to a high defibrillation voltage(e.g., defibrillation voltages up to approximately 1000 Volts) at node310. The energy associated with this high defibrillation voltage istypically stored on a defibrillation energy storage capacitor 315 untildelivered to heart 110 via defibrillation energy delivery circuit 305and defibrillation electrodes 120A–B. While the defibrillation voltagesof up to approximately 1000 Volts generally describes currentapplications, defibrillation voltages may often fall within the range ofapproximately 600 to 800 Volts, such as approximately 780 Volts orapproximately 645 Volts. Regardless, the various embodiments of theinvention are not limited by such defibrillation voltages and may beadapted to other voltages.

Defibrillation energy delivery circuit 305 includes a first inputterminal that receives a first power supply voltage (e.g., the voltageassociated with the defibrillation energy at node 310) and a secondinput terminal that receives a second power supply voltage (e.g., theground voltage at node 320). Energy delivery circuit 305 includes anH-bridge 325, which includes four switches (i.e., first and secondpull-up switches 330A–B and first and second pull-down switches 335A–B)for coupling the defibrillation energy at node 310 and the groundvoltage at node 320 to first and second output terminals at nodes340A–B, respectively. Nodes 340A–B are coupled to defibrillationelectrodes 120A–B, respectively.

Pull-up switches 330A–B couple the defibrillation energy at node 310 torespective first and second output terminals at nodes 340A–B,respectively. Pull-down switches 335A–B couple the ground voltage atnode 320 to respective first and second output terminals at nodes340A–B, respectively. In one embodiment, for delivering a monophasicdefibrillation energy pulse, control circuit 345 (which canalternatively be conceptualized as part of controller 220) turns onpull-down switch 335A, then turns on pull-up switch 330B. To discontinueenergy delivery, control circuit 345 turns off pull-down switch 335A,thus turning off pull-up switch 330B. To further deliver a biphasicdefibrillation energy pulse, control circuit 345 then turns on pull-downswitch 335B, then turns on pull-up switch 330A. To discontinue energydelivery, control circuit 345 then turns off pull-down switch 335B, thusturning off pull-up switch 330A. Multiphasic energy delivery may begenerated by repeating the cycle of delivering and discontinuing anenergy pulse in similar fashion for three or more cycles. It is thusinherent that the two cycles of biphasic energy delivery are a subset ofthe three or more cycles of multiphasic energy delivery. In oneembodiment, the user can select between monophasic, biphasic ormultiphasic energy delivery using programmer 150 to program device 105to operate accordingly.

In one embodiment, by way of example, but not by way of limitation,pull-down switches 335A–B include insulated gate bipolar transistors(IGBTs) or other switching devices that couple the respective first andsecond defibrillation electrodes 120A–B to ground node 320. In oneembodiment, first pull-down switch 335A includes a collector coupled tofirst defibrillation electrode 120A, a gate coupled to receive controlsignal S1 at node 350 from control circuit 345, and an emitter coupledto ground node 320. Second pull-down switch 335B includes a collectorcoupled to second defibrillation electrode 120B, a gate coupled toreceive control signal S2 at node 355 from control circuit 345, and anemitter coupled to ground node 320.

In one embodiment, by way of example, but not by way of limitation,first and second pull-up switches 330A–B include triacs, thyristors,semiconductor-controlled rectifiers (SCRs), semiconductor-controlledswitches (SCSs), four-layer diodes or other switching devices thatcouple the high voltage associated with the defibrillation energy atnode 310 to first and second defibrillation electrodes 120A–B,respectively. In one embodiment, control signals S3 and S4 are receivedat nodes 360 and 365, respectively, from control circuit 345 to initiateoperation of first and second pull-up switches 330A–B, respectively. Inone embodiment, control signals S3 and S4 activate triggering devices370A–B, which provide triggering signals to the gates of switches330A–B, respectively.

In a further embodiment, first and second pull-up switches 330A–Binclude single-quadrant thyristors. A triac (also referred to as abilateral triode switch) typically latches into a conducting state inthree quadrants of the four quadrants in its current vs. voltage graph.FIG. 4A is a graph illustrating generally, by way of example, but not byway of limitation, one embodiment of a portion of a current vs. voltagecharacteristic of a triac, with the four quadrants labeled I, II, III,and IV. Each of quadrants I, II, and III include a resistive/blockingstate 405 (indicated by a portion of the curve running approximatelyparallel to the voltage axis) and a conductive/latching state 410(indicated by a portion of the curve running approximately parallel tothe current axis). An appropriate trigger current, I_(G), to the gate ofthe triac reduces the breakover voltage magnitude v_(bo) between theresistive and conductive states, allowing the triac to latch into theconductive state. The solid lines generally depict breakover voltage ata trigger current of zero. The dashed lines generally depict the effecton breakover voltage at a trigger current of magnitude greater than zero(absolute value greater than zero for quadrant I and absolute value lessthan zero for quadrants II and III).

By contrast, FIG. 4B is a graph illustrating generally, by way ofexample, but not by way of limitation, one embodiment of a portion of acurrent vs. voltage characteristic of a single-quadrant thyristor. Onlythe third quadrant, quadrant III, includes both a resistive/blockingstate 405 and a conductive/latching state 410 within the range oftrigger currents as described herein. Quadrants I, II, and IV includeonly resistive/blocking states (although it is understood that quadrantII could have a conductive region, albeit without latching; this isimplied, but not shown in FIG. 4B). It is also understood thatsingle-quadrant thyristors for use with the various embodiments of theinvention could provide a conductive/latching state using quadrantsother than the exemplary third quadrant without departing from the scopeof the teachings of this document, provided only one quadrant of thesingle-quadrant thyristor includes both a resistive/blocking state andthe conductive/latching state as described herein.

The gate triggering current for which it is designed latches thesingle-quadrant thyristor in a conductive/latching state in essentiallyonly one quadrant of the current vs. voltage characteristic graph. It isunderstood that it may be possible to conduct through thesingle-quadrant thyristor in other quadrants as well, but that asubstantially larger gate triggering current, i.e., exceeding deviceratings, is required to initiate conduction in those other quadrants.Stated differently, triggering devices 370A–B are designed to sink atrigger current from the gates of switches 330A–B to enable and latchconduction from node 310 to one of respective nodes 340A–B in only asingle quadrant of the current vs. voltage graph. In one example, anegative trigger current to, or a current sink from, each of thesingle-quadrant thyristors 330A–B couples the large positive voltageassociated with the defibrillation energy at node 310 to a respectiveone of electrodes 120A–B.

Single-quadrant thyristors of the type used for the various embodimentsof the invention are also capable of withstanding rapid dV/dttransitions (e.g., 300V/μs minimum). Rapid voltage versus timetransitions (dV/dt) during defibrillation energy delivery occur at nodes120A and/or 120B during turn-on and/or turn-off of pull-down switches335A and/or 335B. Because such single-quadrant thyristors are designedto 1) withstand such dV/dt transitions; 2) provide high voltage blockingcapabilities (e.g., 1200V minimum); and 3) conduct/latch in only onequadrant (e.g., quadrant III), additional semiconductor devices inseries with triac/thyristor devices may be eliminated. This eliminationof such series components in the defibrillation energy delivery circuit305 may reduce the number of processing steps, reduce cost and reducethe physical size of the implantable cardiac rhythm management device.

FIG. 3 also illustrates triggering devices 370A–B, as discussed above.In one embodiment, triggering devices 370A–B include current-limitingswitches such as, for example, high voltage n-channel field-effecttransistors (FETs) that, when turned on by control signals S3 and S4,function in their saturation region of operation. Unlike typical FETdesigns, which provide high drain-source current in saturation, thepresent triggering devices 370A–B of one embodiment are designed with aneffective low transconductance, which provides a relatively lowdrain-source current in saturation.

In one embodiment, this effective low transconductance is obtained byenabling for conduction a preselected number of available parallelconducting channels in triggering devices 370A–B to obtain the desiredtransconductance. In one example, triggering devices 370A–B are powermetal-oxide-semiconductor FETs (MOSFETs) with vertically orientedconducting channels. A gate and source are associated with a first sideof the semiconductor substrate of triggering devices 370A–B, and a drainis associated with an opposing second side of the semiconductorsubstrate of triggering devices 370A–B. A vertical channel is formedthrough the substrate between source and drain under control by thegate. By fabricating the power MOSFET with a plurality ofdrain-to-source channels, a plurality of vertical conducting channelsbecome available. By selecting a predetermined number of the verticalchannels for activation by the associated gate, a desiredtransconductance can be obtained.

The desired transconductance is achieved, based on the turn-on gatevoltage (e.g., approximately between 10 Volts and 12 Volts) provided bycontrol circuit 345, to provide the desired trigger current to latch thesingle-quadrant thyristor switches 330A–B into a conducting and latchedstate. In one embodiment, the first and second current-limiting switchtriggering devices 370A–B each sink triggering currents from therespective first and second single-quadrant thyristor switches 330A–B ofapproximately between 100 and 235 milliamperes, inclusive, such thatthyristor switches 330A–B latch into their conductive states. As anexample, a single-quadrant thyristor switch may have a nominaltriggering current of approximately 80 milliamperes required to latchinto its conductive state. Its associated triggering device may bespecified to have an engineering margin such that the triggering deviceproduces a triggering current in excess of the nominal value, e.g., thetriggering device may sink triggering currents of approximately 100milliamperes in this example. In one particular embodiment, each ofcurrent-limiting FET switches 370A–B provides an on-state forwardtransconductance of less than or equal to approximately 45 milliSiemens.In any case, the first and second current-limiting switch triggeringdevices 370A and 370B are selected to achieve sufficient current sink ata given gate drive to trigger their respective thyristor switch 330A and330B, respectively.

In FIG. 3, current-limiting FETs 370A–B are modeled as gain-degenerateddevices that include respective source-degeneration resistors 375A–B. Itis understood, however, that in one embodiment, source-degenerationresistors 375A–B do not represent resistors separate and distinct fromdevices 370A–B, but merely represent the on-state integrated sourceresistance associated with each of current-limiting FETs 370A–B. Theon-state source resistance and/or forward transconductance is selectedby enabling a predetermined number of available parallel conductingchannels, as discussed above. By using triggering devices 370A–B thatare inherently current-limiting, the need for additional circuits toperform such current-limiting functions is avoided. This reduces thenumber of electronic components required for energy delivery circuit305, which may further reduce the number of assembly processing steps,reduce cost and reduce the physical size of the implantable cardiacrhythm management device.

In one embodiment, defibrillation energy delivery circuit 305 alsoincludes additional electronic components, such as for determiningdefibrillation lead impedance. One example of using such additionalelectronic components for determining defibrillation lead impedance isdescribed in U.S. patent application Ser. No. 09/236,911 to Linder etal., filed Jan. 25, 1999, now issued as U.S. Pat. No. 6,317,628, whichis commonly assigned and incorporated herein by reference.

CONCLUSION

This document describes, among other things, portions of a cardiacrhythm management system including an implantable cardiac rhythmmanagement device that includes a defibrillation energy deliverycircuit. The defibrillation energy delivery circuit provides high sideenergy delivery through a single-quadrant thyristor switch that istriggered by a current-limiting transistor switch. The defibrillationenergy delivery circuit requires fewer electronic components, reducingthe size and/or cost of the implantable cardiac rhythm managementdevice. For example, the single-quadrant thyristor, designed to conductand latch in only one quadrant (e.g., quadrant III) and havingappropriate dV/dt and voltage blocking capabilities, may eliminate theneed for additional series-coupled semiconductor devices. In anotherexample, current-limiting is designed into, or inherent in, thesemiconductor device triggering the single-quadrant thyristor, therebyeliminating the need for additional current-limiting circuits.

It is to be understood that the above description is intended to beillustrative, and not restrictive. Many other embodiments will beapparent to those of skill in the art upon reviewing the abovedescription. For example, while the various embodiments referred tospecific values of voltages, transconductance, triggering currents,etc., such values are at the discretion of the designer and couldinclude values outside the range of the specific examples given. Thescope of the invention should, therefore, be determined with referenceto the appended claims, along with the full scope of equivalents towhich such claims are entitled.

1. An implantable cardiac rhythm management device comprising adefibrillation energy delivery circuit including: an input terminal toreceive defibrillation energy; an output terminal to deliver thedefibrillation energy; and means for delivering the defibrillationenergy from the input terminal to the output terminal, including meansfor conducting and latching in a single quadrant of a current versusvoltage characteristic.
 2. The device of claim 1, wherein the means fordelivering the defibrillation energy includes means for triggering theconduction.
 3. The device of claim 2, further including a switch coupledto the means for triggering the conduction, wherein the switch suppliesa current to trigger the conduction.
 4. The device of claim 3, whereinthe switch is a current-limiting field effect transistor.
 5. The deviceof claim 3, wherein the means for conducting and latching in a singlequadrant includes means for conducting and latching in a third quadrantcorresponding to a negative current and a negative voltage.
 6. Thedevice of claim 1, wherein the means for delivering the defibrillationenergy includes a thyristor.
 7. The device of claim 1, wherein thesystem includes: a second input terminal to receive a power supply; anda switching means to couple the first output terminal to the secondinput terminal.
 8. The device of claim 7, wherein the switching meansincludes insulated gate bipolar transistors (IGBTs).
 9. A cardiac rhythmmanagement device comprising a defibrillation energy delivery circuitincluding: a first input terminal to receive defibrillation energy;first and second output terminals to deliver the defibrillation energy;a first single quadrant thyristor coupled to the first input terminaland the first output terminal; a second single quadrant thyristorcoupled to the first input terminal and the second output terminal; andswitching means coupled to the first and second thyristors to triggerconduction of the thyristors.
 10. The system of claim 9, wherein each ofthe thyrsitors includes a gate, and the switching means is coupled tothe gates of the thyristors.
 11. The system of claim 10, wherein theswitching means sinks a current at the gates of the thyristors.
 12. Thesystem of claim 11, wherein the switching means includes a pull downswitch.
 13. The system of claim 11, wherein the switching means includesa current limiting field effect transistor (NFET).
 14. A method fordelivering energy used in defibrillation therapy comprising: providingdefibrillation energy at an input terminal; and triggering a powersupply coupling switch to conduct and latch current in a single quadrantof a current versus voltage characteristic from the input terminal to anoutput terminal for use in the defibrillation therapy.
 15. The method ofclaim 14, wherein triggering a power supply coupling switch includestriggering a thyristor.
 16. The method of claim 15, wherein triggeringthe thyristor includes enabling third quadrant conduction.
 17. Themethod of claim 15, wherein triggering the thyristor includes providinga current to a gate of the thyristor.
 18. The method of claim 17,wherein providing a current includes limiting the current to apredetermined approximate value.
 19. The method of claim 14, wherein themethod further includes: providing a ground voltage at a second outputterminal; and enabling a pulldown switch to couple the second outputterminal to ground.
 20. The method of claim 19, wherein enabling apull-down switch is executed before triggering the power supply couplingswitch.